Data storage device employing sliding mode control of spindle motor

Abstract

A data storage device is disclosed comprising a head actuated over a disk, and a spindle motor configured to rotate the disk. A speed of the spindle motor is sampled, and an error signal is generated based on a difference between the sampled speed and a target speed. A sliding mode control signal for controlling a speed of the spindle motor is generated based on a first non-zero gain when the error signal is greater than zero and less than a first positive threshold, and a second non-zero gain when the error signal is greater than the first positive threshold.

What is claimed is: 
     
         1 . A data storage device comprising:
 a head actuated over a disk;   a spindle motor configured to rotate the disk; and   control circuitry configured to:
 sample a speed of the spindle motor at a sampling rate; 
 generate an error signal based on a difference between the sampled speed and a target speed; 
 generate a sliding mode control signal for controlling a speed of the spindle motor based on the error signal; and 
 when the error signal exceeds a threshold, increase the sampling rate. 
   
     
     
         2 . The data storage device as recited in  claim 1 , wherein the control circuitry is further configured to:
 sample the speed of the spindle motor based on a back electromotive force (BEMF) voltage generated by the spindle motor;   when the error signal is less than the threshold, sample the speed once per revolution of the disk; and   when the error signal exceeds the threshold, sample the speed at least twice per revolution of the disk.   
     
     
         3 . The data storage device as recited in  claim 2 , wherein:
 the BEMF voltage crosses a threshold at least twice per revolution of the disk; and   the control circuitry is further configured to sample the speed based on a duration between the BEMF voltage crossings.   
     
     
         4 . The data storage device as recited in  claim 1 , wherein the disk comprises a plurality of servo sectors and the control circuitry is further configured to sample the speed of the spindle motor based on the servo sectors. 
     
     
         5 . The data storage device as recited in  claim 4 , wherein the control circuitry is further configured to sample the speed based on a duration between the servo sectors. 
     
     
         6 . A method of operating data storage device, the method comprising:
 sampling a speed of a spindle motor at a sampling rate;   generating an error signal based on a difference between the sampled speed and a target speed;   generating a sliding mode control signal for controlling a speed of the spindle motor based on the error signal; and   when the error signal exceeds a threshold, increasing the sampling rate.   
     
     
         7 . The method as recited in  claim 6 , further comprising:
 sampling the speed of the spindle motor based on a BEMF voltage generated by the spindle motor;   when the error signal is less than the threshold, sampling the speed once per revolution of the disk; and   when the error signal exceeds the threshold, sampling the speed at least twice per revolution of the disk.   
     
     
         8 . The method as recited in  claim 7 , wherein:
 the BEMF voltage crosses a threshold at least twice per revolution of the disk; and   the method further comprises sampling the speed based on a duration between the BEMF voltage crossings.   
     
     
         9 . The method as recited in  claim 6 , wherein the disk comprises a plurality of servo sectors and the method further comprises sampling the speed of the spindle motor based on the servo sectors. 
     
     
         10 . The method as recited in  claim 9 , further comprising sampling the speed based on a duration between the servo sectors.